In the field of operation processors, progresses in semiconductor manufacturing techniques have brought about dramatic advancements in processing performance speed and functionality. On the other hand, in line with downsizing trends, case sizes are decreasing. While functionality has improved and sizes have decreased, power consumption by operation processors has increased, and the amount of heat generated is becoming greater than had been conventional. There is a problem in that, as a common property of semiconductors used in operation processors, their power consumption becomes greater the faster they operate, while they are susceptible to heat and failures increase when they are used under high temperatures. For this reason, in order to advance the high-functionality and size reduction of operation processors, progress in power saving techniques as well as cooling techniques have become indispensible in recent years.
As cooling methods for operation processors, natural cooling using natural circulation of air, and forced cooling in which cooling is performed by rotating a fan to generate a flow of air are common. Natural cooling is a cooling method that has been known for a long time, and while it can be accomplished with a simple mechanism, its cooling effects are limited. Forced cooling is a method in which a wind is generated by rotating a fan to enhance cooling effects. However, to the extent that a fan is required, the mechanism is made more complex.
For operation processors as represented by blade servers, etc., fan-based forced cooling methods are generally used. Such operation processors allow a plurality of operation units and Input/output units, which are cooling targets with built-in heat generating bodies, to be mounted, and comprise a plurality of fan boxes for cooling them. Further, taking serviceability into consideration, a typical structure would have a blade part disposed at the front face of a case, and an Input/output unit and a fan box disposed at the case rear face on top of each other and in parallel. With respect to the cooling method, a method is adopted in which external fresh air is made to hit the blade part with a built-in heat generating body, and the cooling wind that has been discharged after cooling the blade part is made to hit the Input/output unit and is vented from the fan box.    Patent Document 1: JP Patent Publication (Kokai) No. 2001-189584 A